CaveEntrance
A cave entrance, that acts like either up stairs or down stairs depending on whether
it is outside or inside (being a cave entrance, it must be the means to move between
an outside and an inside map).

EuclideanTransporter
This is a special transporter that has complicated activation requirements (exactly
for Euclidean Engines need to be activated on the board before this transporter will
switch from the off to the on state, and allow the player to transport).

Exchanger
When the player walks into an exchanger, the item the player is holding is
exchanged with the piece on the other side of the exchanger.